1. Field of the Invention
This invention relates to a hydrogenation catalyst and a hydrogenation process wherein said catalyst is used. More particularly, this invention relates to a hydrogenation catalyst and to a process wherein said catalyst is used to saturate ethylenic and/or aromatic unsaturation.
2. Prior Art
Catalyst for hydrogenating chemical compounds containing ethylenic and/or aromatic unsaturation, are, of course, well known in the prior art. Useful catalysts include such heterogeneous catalysts as nickel on kieselguhr, Raney nickel, copper chromate, molybdenum sulfide, finely divided platinum, finely divided palladium, platinum oxide, copper chromium oxide and the like, as taught, for example, in U.S. Pat. No. 3,333,024. Useful catalysts also include homogeneous systems such as those prepared with rhodium compounds or complexes, as taught, for example, in U.K. Patent No. 1,558,491 and in U.S. Pat. Nos. 4,581,417 and 4,674,627 and those prepared with ruthenium complexes as taught, for example, in U.S. Pat. No. 4,631,315. As is known in the prior art, certain of these catalysts are quite effective in the hydrogenation of ethylenic unsaturation but many of these catalysts are not particularly selective as between ethylenic and aromatic unsaturation and therefore cannot be effectively used to selectively hydrogenate ethylenic unsaturation in a compound containing both ethylenic and aromatic unsaturation. Moreover, certain of these catalyst are not, generally, practical for use in large scale commercial operations where catalyst recovery is inefficient as in polymer hydrogenation processes. In this regard, it should be noted that the precious metals used in certain of these catalysts are available only in limited supply which makes these catalysts very costly when compared to the costs of these catalysts commonly used in polymer hydrogenation processes.
Catalysts which are useful in the hydrogenation of ethylenic unsaturation, which catalyst may be used selectively as between ethylenic and aromatic unsaturation, also include catalysts which are frequently referred to as homogeneous systems, prepared by combining an iron group metal compound, particularly a nickel or cobalt compound, with a reducing agent. Such catalyst may be the reaction product of an iron group metal alkoxide and an aluminum hydrocarbon compound as taught, for example, in U.S. Pat. No. 3,113,986; the reaction product of an iron group metal carboxylate, chelate or alkoxide and a lithium or magnesium hydrocarbon compound as taught, for example, in U.S. Pat. No. 3,541,064., the reaction product of a nickel or cobalt alkoxide or carboxylate and an aluminum trialkyl as taught, for example, in U.S. Pat. No. 3,700,633 or the reaction product of an iron group carboxylate, an enolate, a phenolate or a salt of certain sulfur-containing acids and half esters thereof and a metal alkyl of a metal selected from Groups I, II and III as taught for example in British Patent Specification 1,030,306. It is also known to use iron group metal compounds containing from about 0.4 to about 1.3 mols of water per mole of iron group metal compound in preparing catalysts of this type. Reducing agents that may be used in preparing catalysts include metal alkoxides as taught, for example, in U.S. Pat. Nos. 3,412,174 and 4,271,323. As is known in the prior art, these catalysts can be used in a manner such that essentially all of any ethylenic unsaturation contained in the chemical compound is hydrogenated while essentially none of the aromatic unsaturation contained therein is hydrogenated. These catalysts, are, however, generally, less active than the non-selective catalysts heretofore known in the prior art, and, as a result, longer holding times are required to effect the desired degree of selective hydrogenation. Moreover, most, if not all, of these selective catalysts generally result in significant conversion of ethylenic unsaturation in relatively short contacting times and then proceed rather slowly with respect to such conversion thereafter, thereby preventing good control over the extent of conversion of the ethylenic unsaturation when partial hydrogenation is the desired objective.
In light of these deficiencies of the prior art hydrogenation catalysts, then, the need for a catalyst which can be used to selectively hydrogenate ethylenic unsaturation in a chemical compound containing both ethylenic and aromatic unsaturation, which catalyst may be prepared with metals that are more readily available and which catalyst will provide greater hydrogenation after a reasonable contacting time when compared to the selective catalyst known in the prior art, is believed to be readily apparent. The need for a catalyst which will afford better control over the extent of hydrogenation is also believed to be readily apparent.